Which one of the following is an amphoteric oxide?

Amphoteric oxides react with both acids and bases to form salt and water. Aluminium oxide (Al2O3) is a classic amphoteric oxide — it reacts with HCl to form AlCl3 and with NaOH to form sodium aluminate (NaAlO2). MgO and Na2O are basic oxides (reacting only with acids), while P4O10 is an acidic oxide (reacting only with bases to form phosphates). Hence Al2O3 is the amphoteric oxide.